1. Field of the Invention
The present invention relates to a rotor.
2. Discussion of the Background
Rotors for permanent-magnet motors that have been lightened to reduce their weight are well known (for example, Japanese Patent No. 3954018).
A conventional rotor that has been lightened is briefly described below with reference to FIG. 8. A rotor 100 includes a cylindrically shaped hub 101 secured to an output shaft, an annularly-shaped rotor core 102 disposed radially outward of the hub 101, and a plurality of ribs 103 that connect the hub 101 and the rotor core 102, all of which are integrally formed into one piece where a section between the hub 101 and the rotor core 102 is provided with a plurality of holes 104. Such holes 104 are known as lightening holes. Magnetic poles 105 and salient poles 106 are alternately disposed on the circumference of the rotor core 102 along the circumferential direction, and permanent magnets 108 are fitted in and secured to openings 107 formed in the magnetic poles 105.
Grooves 109 extending radially inward from the circumference of the core 102 are each formed between the magnetic poles 105 and the salient poles 106 that neighbor each other. In other words, the salient pole 106 is provided between a pair of the grooves 109. The holes 104 have the same shape, and a wall surface (namely, inner circumferential surface 110 of the rotor core) disposed radially outward of the hole 104 is formed in an arc-like surface along a circle concentric with the hub 101 and the rotor core 102.